Question

I am using the reachability code from apple to find if my iphone is connected to the wifi. Next i would like to list all the devices that are in my wifi range. How should i do this. The other devices do not publish any service. I want to detect all devices in my wifi range and send that device a request for tcp connection.

Answer 1

As @Alex says, even if you could find devices that weren t advertising, what s the point? You can t most likely do any adhoc communications with them. Instead you d need to find copies of your application running on connected devices, and your app needs to advertise.

Take a look at Gamekit sample projects which will give you bluetooth connectivity, and you could dig into something like Jens Alfke s MyNetwork and Blip libraries for tcp/wifi. http://jens.mooseyard.com/2008/05/blip-come-n-get-it/

Answer 2

If a device does not advertise its presence and is not otherwise active, TCP/IP does not give you a way to "detect" it. If you can identify your subnet (which has nothing to do with a "wifi range", whatever that may be), you can try connecting to each possible host in it on all possible ports -- this is generally considered an attack (what legitimate reason could you have for such a port scan?), so, if you re detected trying this attack, be prepared for the consequences.

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